Tank

ABSTRACT

The invention provides a tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel wherein the vessel has substantially planar sides. The vessel can be substantially quadrilateral. At least a part of the bottom of the vessel can be canted with respect to the sides of the vessel. The invention can also provide a tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel, the frame having a top and a base wherein the vessel is retained in the frame by removable keys that connect the top of the frame to the base.

This invention relates to a tank, particularly one adapted to contain, store and transport fluids such as chemicals. Particular embodiments of the tank of the present invention find utility in the offshore oil and gas industry, to contain, store and transport fluids to the rigs, and optionally to contain, store and transport fluids recovered from the wells during drilling and production operations.

According to the present invention there is provided a tank for storing fluids, comprising a flat-sided vessel and a reinforcing frame extending over all of the flat sides of the vessel.

The present invention also provides a tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel, wherein the top of the tank can be accessed from ground level.

Typically the flat-sided vessel is generally square in cross-section, but can be of any quadrilateral shape, and has a flat top and bottom. The flat sided vessel can be rectangular in cross section.

The flat sides of the vessel enable the use of bracing frames constructed from flat members thereby enhancing the strength of the assembly, and making the tank less susceptible to variations in tolerance.

Typically at least a part of the bottom of the vessel is canted with respect to the sides of the vessel.

The bottom of the vessel can have two portions, and both of these can be canted at an angle greater than 90° with respect to the sides of the vessel, so that they meet at an apex on the bottom of the vessel that is at the lowest point of the vessel in use. Typically a first portion is canted at a shallow angle with respect to the side walls, typically between 90° and 95°, e.g. typically 91°, 92°, 93°, 94° or 95° and typically a second portion is canted to a greater extent, typically at an angle between 120° and 150°, e.g. preferably 135°+/−5°.

At the apex of the bottom of the vessel where the first and second portions are connected together at the lowest point, the vessel typically has an outlet for fluids. Siting the outlet of the vessel at the apex as in this manner has the advantage that fluids drain easily from the outlet, and complete drainage of the vessel can be facilitated.

The bottom of the vessel can be formed from more than two portions, and such portions can similarly be canted towards the apex. This also improves the drainage of fluid from the vessel.

In some favoured embodiments, the first portion of the bottom of the vessel is canted at around 92° or 93° with respect to the rear of the vessel so as to create a gentle downward slope on the bottom of the vessel that is as close to horizontal as possible while still encouraging fluid to drain from the sidewalls toward the outlet at the apex between the first and second portions. The second portion is typically canted at around 135° with respect to the front of the vessel, and this typically creates a recess between the square frame and the front of the vessel in the area of the outlet, which can therefore accommodate hoses, valves, connectors, pumps etc that may be used to extract fluids from the vessel during use.

The bottom of the vessel can be formed from four portions. Each portion can be canted at an angle greater than 90° relative to its respective side wall. Two of the portions can be canted by the same degree from and with respect to opposing side walls. The remaining two portions can be canted at different angles with respect to one another. An outlet can be provided at the lowest point, typically at the apex of the portions.

Typically, the vessel is removable from the frame that surrounds it. The frame can be made up of hollow beams or box sections that are welded together, and in some embodiments, the frame has a lower basket formed by four sides and a base, and a top section that is removably secured to the basket after the vessel is placed in the basket. In such embodiments, the basket can be generally square, with a generally flat base and sidewalls, although in some embodiments the inner surface of the base can allow for the slight degree of canting applied to the first section of the tank, so as to support the first section of the bottom of the tank along its length.

According to other embodiments, the frame can be provided with a removably securable side portion. The side portion can be provided with one or more brackets that are arranged to overlap beams making up the frame. Fixing means can be inserted through the overlapping portion of the brackets and beams to removably secure the side portion to the frame. Use of a removable side portion is advantageous in that it allows fewer securing bolts to be used than a removable top portion.

In various embodiments of this type, the vessel can be mounted on a sub-frame provided on the base portion and canted to the same degree as the first portion of the vessel, so as to support the vessel within the frame from beneath. In some favoured embodiments, the outer surface of the frame is generally a regular shape (e.g. square) in cross and transverse sections, so that multiple frames can be stacked on top of one another to permit easy storage, handling and movement of the tanks.

Typically only the inside surface of the frame (e.g. the sub-frame) is canted to match the outer surface of the vessel, and the outer surface of the frame is typically a regular quadrilateral shape with 90° corners.

The frame can have stacking posts and recesses provided to facilitate stacking of the frames on top of one another.

Each corner of the top portion of the frame can be provided with a stacking post extending diagonally inwardly and upwardly from the frame. The base portion can be provided with corresponding recesses for receiving the stacking posts so that frames can be easily stacked on top of one another. The stacking posts can be in the form of padeyes to facilitate the lifting of frames using conventional equipment.

In favoured embodiments of the invention, the vessel can be a tight fit within the frame, so that any loads applied to the vessel (for example by volatile fluids within the vessel stored under pressure) will be transferred to the frame. This means that the loads do not need to be contained by the vessel itself, which can therefore be engineered to a lower specification, and can rely on the frame to deal with the loads and stresses applied by normal use.

In some embodiments, the corners of the vessel can be rounded, chamfered, or recessed away from the corners of the frame so that loads are not transferred between the corners of the frame and the corners of the vessel. A similar gap can be left at all corners of the vessel and frame.

The top section of the frame is typically received within an aperture in the basket and is usefully removable and detachable from the basket. This allows removal of the vessel from the frame to replace or maintain the vessel or the frame without affecting the other. Typically the vessel is held within the frame by one or more keys that are typically connected between the top section and the basket of the frame once the vessel is in place within the basket. Typically each key takes the form of a bar extending between the top and basket portions of the frame, and can optionally be held in place by a welded plate preventing removal of the key, and thereby securing the two portions of the frame together, and holding the vessel in place within the basket. This feature forms an independent aspect of the invention, which provides a tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel, wherein the vessel is retained in the frame by removable keys that optionally connect the top of the frame to the base.

Some embodiments of the tank of the invention can be insulated, and insulation is typically provided in the form of a cover for the vessel. The cover can surround the vessel within the frame, and useful covers can be formed from rubber or similar resilient and insulating material.

In addition to the rubber cover over the internal vessel, insulation can be applied to the tank between the beams of the frame, and this can be held between inner and outer plates on the frame. Typically the insulation is foam or rock wool insulation, and can be riveted between inner and outer plates welded in the apertures between the beams of the frame. In preferred embodiments, the inner plates are recessed from the inner surface of the frame, so that the vessel bears against the frame and not the inner plate. The plates therefore need only hold the insulation in place and do not need to bear any of the forces normally exerted on the frame.

A pressure release valve and/or an airline valve can be provided towards the top portion of the vessel for aiding drainage.

The tanks and vessels can be provided in different sizes to hold varying quantities of fluid. For example, the capacity of the vessels can range between 500 and 1000 gallons.

An embodiment of the invention will now be described, by way of example, and with reference to the accompanying drawings, in which:

FIG. 1 shows a front view of a tank according to the invention;

FIG. 2 shows a side view of the FIG. 1 tank;

FIG. 3 shows a rear view of the tank;

FIGS. 4 and 5 show plan views of the tank;

FIG. 6 shows a plan view of the basket of the frame of the FIG. 1 tank;

FIG. 7 shows a side view of the FIG. 6 base;

FIG. 8 shows a plan view of the base and sides of the tank;

FIG. 9 shows a side view of the FIG. 8 base and sides;

FIGS. 10, 11 and 12 show side, rear and front views of the FIG. 8 frame;

FIG. 13 is a plan view of a top section of the frame;

FIG. 14 is a sectional view through the FIG. 13 top section at line A-A;

FIGS. 15 and 16 show side and plan views of locking pins used to retain the FIG. 13 top section within the basket;

FIG. 17 is a front view of a vessel used in the tank;

FIG. 18 is a side view of the vessel; and

FIG. 19 is a plan view of a portion of the top of the FIG. 17 vessel.

FIGS. 20, 21 and 22 are front, side and rear views of a tank according to another embodiment of the invention;

FIG. 23 is a plan view of the base of the tank of FIG. 20;

FIG. 24 is a plan view of the top of the tank of FIG. 20;

FIG. 25 is a plan view of the top of a tank with a walkway positioned thereon;

FIGS. 26, 27 & 28 are front, side and plan views of the base of the frame of the tank of FIG. 20;

FIGS. 29, 30 & 31 are front, side and rear views of the frame;

FIG. 32 is a plan view of the frame;

FIG. 33 is a plan view of a corner gusset of the frame;

FIG. 34 is a side view of a lower end plate of the frame;

FIG. 35 is a side view of the portion of removable frame;

FIGS. 36 & 37 are partial side and end views of the side portion attached to the frame;

FIGS. 38 & 39 are partial side and plan views of a padeye in the top portion of the frame;

FIG. 40 is a side view of a padeye;

FIGS. 41 & 42 are front and plan views of the top portion of the frame;

FIGS. 43 & 44 are side and rear views of a top portion of the frame;

FIG. 45 is a sectional view of landing edges and a door frame;

FIG. 46 is a plan view of the tank with a walkway;

FIG. 47 is a top view of a main panel of the walkway;

FIG. 48 is a top view of a door of the walkway;

FIGS. 49 and 50 are sectional side and rear views of a base portion of the tank;

FIGS. 51 and 52 are sectional rear and side views of a support;

FIGS. 53 and 54 are front and side views of the vessel;

FIG. 55 is a plan view of the vessel;

FIG. 56 is a partial plan view of a corner of the vessel;

FIG. 57 is a detailed view of the discharge valve of the vessel; and

FIG. 58 is a partial side view of a base of the tank.

Referring now to the drawings, a tank of the invention has a frame and a vessel 50. The frame is constructed from box section beams of 8 mm stainless steel, and useful materials include Strongbox, Hybox and similar configurations of beams. The frame comprises a basket 5 and a top section 5 t. The basket 5 has four corner posts 6, an upper rail 7, a middle rail 8, and a base rail 9. The upper, middle and base rails all extend between corner posts 6. The top of each corner post 6 has a padeye 6 p for lifting. The upper rail 7 has a pair of stacking posts 7 p at the front and back of the basket, that engage within recesses (not shown) in the underside of the base rail 9 of adjacent tanks.

The upper, middle and lower rails are braced by cross braces 11 in the various patterns shown in the drawings. The pattern of cross bracing is not crucial, and different patterns can be used if desired. A ladder can be formed by rungs welded between the cross-braces 11 if desired. The rungs, cross-braces and upper surfaces of the rails can be provided with anti-slip surfaces to facilitate climbing on the tank, although most actions can typically be performed on the tank shown in the drawings by accessing it from ground level without requiring climbing, which is a great safety benefit.

The base of the basket 5 (shown in FIGS. 6 and 7) is formed by the base rails 9, a pair of fork pockets 12 which extend from the front to the back of the base, and a central strut horizontal 10 which extends between the two side rails 9 of the base, and braces the fork pockets 12 against lateral loads. The strut 10 is typically formed in three parts disposed between the fork pockets 12 and the side rails 9, although a single strut could be welded to the lower or upper surface of the fork pockets and rail 9 if desired. Likewise the base rail 9 at the front and back of the tank is divided into three parts a, b and c, as shown in FIGS. 6 and 7, which brace between the fork pockets 12 at the front and back of the tank for the same reason. The front base rails 9 could be solid like the side base rails and alternative strut embodiment if desired, but interposing the rails and the fork pockets 12 protects the fork pockets 12 from lateral loads which could deflect them.

The vessel 50 rests within the basket 5 on a base sub-frame 20, shown in FIGS. 9 and 10, which is welded to the fork pockets 12, the cross-braces 11 and the corner posts 6. The sub-frame 20 has a first portion 20 a that is canted at an angle of around 91-95° with respect to the vertical corner posts, so that the first portion 20 a of the sub-frame slopes downward from the back of the tank toward the front. The sub-frame has a second portion 20 b comprising four struts that are welded between the foremost part of the first portion 20 a and the middle rail 8 at the front of the tank, and are canted upward from the first portion 20 a at an angle of around 135° with respect to the vertical corner posts 6.

The vessel 50 (FIGS. 17-19) has parallel sides 52, a top 54 and a base 56. The top is welded to the sides at generally right angles thereto. The base is formed from first and second portions 56 a and 56 b. First portion 56 a is canted at an angle of 92° to the back wall 52 b and corner posts 6, and slopes downward from the back of the tank to the front. The second portion 56 b of the base is canted at an angle of 135° to the front wall 52 f and corner posts 6 and is welded to the first portion at an apex 56 x, which coincides with the lowest portion of the vessel in use. When the vessel is in place in the basket, the first portion of the vessel base 56 a is supported by the first portion of the frame base 20 a, and the second portion of the vessel base 56 b is supported by the second portion of the frame base 20 b. In practice the angles of the first and second portions of the bases 20 and 56 are matched so that the vessel is supported by the frame with a close tolerance, and so that gaps between the two are minimised. The actual angle is not particularly important.

At the centre of the apex joint 56 x the tank has an outlet 60 for draining the vessel 50. When the tank is resting on a horizontal surface with the vessel 50 in place in the frame as shown in FIG. 2, the outlet 60 is disposed at the lowest point of the vessel 50, by virtue of the cant in the first and second portions of the base 56. Thus the vessel 50 can drain acceptably under gravity, without necessarily requiring washing or suction to remove the contents.

The top 54 of the vessel 50 has a manhole 62 set into a reinforcing plate 64, a pressure relief valve 66 to vent fluids from the vessel above a set pressure, and a ball valve 68 to permit air to flow into the vessel when the fluids are draining from the outlet 60.

The corners of the vessel 50 are rounded or chamfered at 51, so that a gap is left between the vessel 50 and the frame when the vessel 50 is in place within the basket 5. This is to space the corners of the vessel from the frame so that loads applied to the frame in use (e.g. impacts from other frames during lifting operations) are not transferred from the frame to the weaker vessel.

The top section 5 t of the frame comprises an L-shaped outer rim 30, with an inward-facing ledge 301. The ledge 301 supports an inner grid of box-section beams (typically made from Strongbox or Hybox like the basket) comprising a central square 32 within the outer rim 30, and outer bracing beams 33 interposed between them. The top section is accommodated within the upper aperture of the basket, and overlies the vessel 50 in use, so that the inlet 62 of the vessel 50 is accessible through the central square 32.

The inner grid has a key socket 35 welded to the underside of each bracing beam 33, so that a pair of key sockets and bracing beams is provided on each side of the top section 5 t. Each key socket 35 comprises a box-section beam with a square cross-section that can accommodate within it a key 37 comprising a box-section of slightly smaller diameter. The keys 37 can optionally have a shim pad 38 on one side (not necessarily the top of the key as shown in the drawings) to take up any play between the key and the socket.

In use, when the vessel 50 is in place in the basket, the top section 5 t is placed on-top of the vessel 50 so that the outer rim 30 of the top section 5 t is co-planar with the upper rail 7, and the upper surface of the rail 7 and the top section are generally flush. In this position, the key sockets 35 lie in a plane beneath the rail 7, and the keys 37 can be inserted into the open ends of the sockets 35 from the spaces between the struts 11 and the rails 6 and 7. When so inserted, the ends of the keys 35 protrude from the open ends of the sockets 37 at a level beneath the rail 7, thereby restraining the top section against upward movement out of the basket. In the embodiment shown in the drawings, the outermost end of the key 37 can be welded to a pad 39 connected to the rail 7, so that the key 35 is retained in the socket 37, and thus the top section 5 t is locked to the basket. Other means of keeping the key in the socket can be used. The key is typically square so that it can be rotated about its axis, which permits different orientations of the shim pad 38 in order to optimise the tolerance between the key 37, the socket 35 and the rail 7. To remove the vessel 50 from the basket 5, the pads 39 are cut from the rail 7, and the keys 35 are removed from the sockets 37, thereby allowing the top section 5 t to be lifted from the basket.

FIGS. 20-58 show an alternative embodiment of the invention. FIG. 20 shows a tank having a frame and a vessel 150 within the frame. According to this embodiment the vessel has a capacity of around 600 gallons. The top of the tank is accessible from ground level. The frame can be constructed from box section beams similar to those previously described for the first embodiment.

The frame has an upper rail 107, a middle rail 108, a base rail 109 and four corner posts 106. The rails 107, 108, 109 extend between and are perpendicular to the corner posts 106. The top of each corner post 106 has a padeye 106 p (FIG. 40) for lifting. The padeye 106 p extends diagonally inwardly of the frame and upwardly as shown in FIGS. 38 and 39. The padeye 106 p also acts as a stacking post and can engage with padeye-shaped recesses (not shown) in the underside of the base rail 109 of an adjacent tank. The corners of the frame can be provided with reinforcing gussets 185.

The upper 107, middle 108 and lower 109 rails are braced by cross-braces 111 which reinforce the frame. As previously described, the rails and cross-braces 111 can be provided with anti-slip surfaces to facilitate climbing.

The base of the frame is shown in FIGS. 26 to 28 and has two cross struts 109 b extending from the front base rail to the rear base rail 109. The cross struts 109 b have a fork pocket 112 extending therethrough. A central base strut 109 c extends between the two cross-struts 109 b parallel to and towards the front base rail 109 and can provide additional support to brace the fork pockets 112 against lateral loads. Two smaller struts 109 a are provided extending from each side base rail 109 to the cross-base strut 109 b.

The rear view of FIG. 31 shows an opening in the frame which receives the vessel 150 therethrough. The vessel 150 can then be secured in place within the frame by fixing a side portion 180 in place over the opening. FIGS. 35 to 37 show views of the side portion 180 which can be removably secured to the side of the frame. The removable side portion 180 includes two transverse bars 180 a joined at each end by two end posts 180 b and reinforced with vertical supports 180 c substantially parallel to the end post 180 b. A lower bracket 181 l protrudes from the lower end of each end post 180 b. The upper transverse bar 180 a has two upper brackets 181 u extending upwardly therefrom. The lower brackets 181 l are arranged to be bolted through an end plate 183.

In use, when the vessel 150 is in place in the frame, the side portion 180 is bolted to the frame through the upper and lower brackets 181 u, 181 l attached to the side portion 180.

In use the vessel 150 rests on a base of the frame 120 shown in FIGS. 49 to 52. The base of frame 120 comprises a series of supports. A first support 120 a with an inclined surface 122 is shown in FIGS. 49 and 52. The base of the first support 120 a is welded to cross-struts 109 a and the upper surface is inclined from the front of the vessel to the rear of the vessel and also from the interior of the vessel to the side of the vessel. This front to rear and side to side inclination corresponds with the inclination of the base of the vessel 150. The first support 120 a has brackets 121 a, 121 b, 121 c which reinforce and support the inclined surface 122. A second support 120 b is welded to a base rail 109 on each side of the frame and the middle rail 108 at the front of the frame.

The vessel is shown in more detail in FIGS. 54-58. The vessel 150 has parallel sides 152, a top 154 and a base 156. The top 154 is substantially perpendicular to the sides 152 and the base 156 is formed in four flat portions. Each portion extends along the full length of one of the side walls 152. A first portion of the base 156 a is inclined with respect to the first sidewall 152 a. The first portion 156 a is canted at a shallow angle with respect to the side wall 152 a and slopes downward from the back to the front of the vessel 150. The second portion 156 b is canted more steeply with respect to the second side wall 152 b. Third and fourth portions of the base 156 b, 156 d are canted an angle of 95° with respect to the respective side walls 152 c, 152 d. The outlet 160 is positioned at the lowest point at the base of the vessel 150.

When the vessel 150 is in place on the sub-frame 120, the first portion 156 a of the base and the third portion 156 c are supported by the first sub-frame support 120 a. Another first sub-frame support 120 a is provided on the other side of the vessel 150 and supports the first portion 156 a and the fourth portion 156 d. The second support 120 b is used to support the second portion of the base 156 b. When the tank is resting on a horizontal surface with the vessel 150 supported by the sub-frame 120, the outlet 160 is disposed at the lowest point of the vessel 150 by virtue of the four canted portions of the base 156. Thus, the vessel 150 can drain under gravity more effectively.

The top 154 of the vessel 150 has a manway 162 set into a reinforcing plate 164, a dipstick 163, a pressure relief valve 166 to vent fluids from the vessel above a predetermined pressure and a ball valve 168 to permit air into the vessel when fluids are draining from the outlet 160. The corner of the vessel 150 has chamfered or rounded edges 151 so that there is a gap between the vessel 150 and the corners of the frame when the vessel is in place within the frame. The chamfered or rounded edges 151 restrict impacts experienced during lifting operations from being transferred to the vessel 150 from the frame. The base rail 109 of the frame has a valley 109 v through a central region thereof to facilitate access to the outlet 160.

A walkway 170 (FIGS. 25, 46-48) is provided to cover the top of the vessel 150. The walkway 170 is supported by the roof of the frame. The roof has roof bars 193. A doorway 190 is landed over the manway 162 by landing edges 191. The walkway 170 is constructed of several panels 195 that compartmentalise the tank and allow selective access to features such as the pressure relief valve 166. The walkway 170 also includes two hinged door panels 196 positioned above the manway 162 to allow access thereto. The panels 195 can be secured using standard latches and closing features, the top of which are preferably coplanar with the panels 195.

A document holder 124 (FIG. 20) is provided attached to the frame and remaining within the boundary of the frame. The internal faces of the frame that come into contact with the vessel 150 are carbon steel and provided with a 4 mm semi-hard rubber facing by use of a suitable adhesive. This rubber coating ensures that all carbon steel surfaces coming into contact with the vessel 150 have a protective cushion to prevent galvanic corrosion.

Modifications and improvements can be incorporated without departing from the scope of the invention. 

1. A tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel wherein the vessel has substantially planar sides.
 2. A tank for storing fluids according to claim 1, wherein the vessel is substantially quadrilateral.
 3. A tank for storing fluids according to claim 1, wherein the vessel is substantially square in cross-section.
 4. A tank for storing fluids according to claim 1, wherein a top portion of the tank is accessible from ground level.
 5. A tank for storing fluids according to claim 1, wherein at least a part of a bottom of the vessel is canted with respect to the sides of the vessel.
 6. A tank for storing fluids according to claim 5, wherein the bottom of the vessel has two portions and each portion is canted at an angle greater than 90° with respect to the sides of the vessel, so that the portions meet at an apex on the bottom of the vessel that is at the lowest point of the vessel in use.
 7. A tank for storing fluids according to claim 6, wherein a first portion of the bottom of the vessel is canted at a shallow angle with respect to the side walls.
 8. A tank for storing fluids according to claim 7, wherein the first portion is canted at an angle between 90° and 95°.
 9. A tank for storing fluids according to claim 7, wherein a second portion is canted at a greater angle with respect to the side walls than the first portion.
 10. A tank for storing fluids according to claim 9, wherein the second portion is canted at an angle between 120° and 150°.
 11. A tank for storing fluids according to claim 6, wherein the vessel has an outlet for fluids at the apex of the bottom of the vessel where the two portions are connected together at the lowest point.
 12. A tank for storing fluids according to claim 11, wherein the second portion is canted at around 135° with respect to the front of the vessel, thereby creating a recess between the frame and the front of the vessel in the region of the outlet.
 13. A tank for storing fluids according to claim 1, wherein the bottom of the vessel can be formed from three or more portions, and such portions are canted towards an apex.
 14. A tank for storing fluids according to claim 13, wherein the bottom of the vessel is formed from four portions, wherein two portions are canted by the same degree from and with respect to opposing side walls and the other two portions are canted at different angles.
 15. A tank for storing fluids according to claim 1, wherein the vessel is supported by a base portion of the frame and removable from the surrounding frame.
 16. A tank for storing fluids according to claim 1, wherein the frame is made up of hollow beams or box sections that are welded together.
 17. A tank for storing fluids according to claim 1, wherein the frame has a lower basket formed by four sides and a base.
 18. A tank for storing fluids according to claim 17, wherein the frame has a top portion removably securable to the basket after the vessel is placed in the basket.
 19. A tank for storing fluids according to claim 17, wherein the basket is substantially square, with a substantially planar base and sidewalls.
 20. A tank for storing fluids according to claim 1, wherein a side portion of the frame is selectively detachable.
 21. A tank for storing fluids according to claim 16, wherein at least a portion of an inner surface of the base portion is complementary with the degree of canting applied to the bottom of the tank, so as to support the bottom of the tank along its length.
 22. A tank for storing fluids according to claim 16, wherein the vessel is mounted on a sub-frame provided on the base portion that is canted to the same degree as the first portion of the vessel, so as to support the vessel within the frame from underneath.
 23. A tank for storing fluids according to claim 21, wherein the inside surface of the frame the sub-frame is canted to match the outer surface of the vessel.
 24. A tank for storing fluids according to claim 1, wherein an outer surface of the frame is a substantially regular shape in cross and transverse sections, so that multiple frames can be stacked on top of one another.
 25. A tank for storing fluids according to claim 1, wherein the outer surface of the frame is a regular quadrilateral shape with 90° corners.
 26. A tank for storing fluids according to claim 1, wherein the frame has stacking posts and recesses to facilitate stacking of the frames.
 27. A tank for storing fluids according to claim 26, wherein each stacking post extends diagonally inwardly and upwardly from a top portion of the frame.
 28. A tank for storing fluids according to claim 26, wherein each stacking post is in the form of a padeye.
 29. A tank for storing fluids according to claim 1, wherein the vessel is a tight fit within the frame, so that any loads applied to the vessel are transferred to the frame.
 30. A tank for storing fluids according to claim 1, wherein the corners of the vessel are chamfered away from the corners of the frame so that loads are not transferred between the corners of the frame and the corners of the vessel.
 31. A tank for storing fluids according to claim 15, wherein the vessel is held within the frame by one or more keys that extend between the top portion and the base portion of the frame when the vessel is in place within the frame.
 32. A tank for storing fluids according to claim 31, wherein each key takes the form of a bar extending between the top and base portions of the frame, and is held in place by a welded plate preventing removal of the key, thereby securing the two portions of the frame together, and holding the vessel in place within the frame.
 33. A tank for storing fluids according to claim 1, wherein the tank is insulated.
 34. A tank for storing fluids according to claim 32, wherein a cover is provided for the vessel to surround the vessel within the frame.
 35. A tank for storing fluids according to claim 34, wherein the cover is formed from rubber or similar resilient and insulating material.
 36. A tank for storing fluids according to claim 33, wherein the insulation is applied to the tank between beams of the frame, and held between inner and outer plates on the frame.
 37. A tank for storing fluids according to claim 36, wherein the insulation is foam or rock wool insulation.
 38. A tank for storing fluids according to claim 37, wherein the insulation is riveted between inner and outer plates welded in the apertures between the beams of the frame.
 39. A tank for storing fluids according to claim 37, wherein the inner plates are recessed from the inner surface of the frame, so that the vessel bears against the frame.
 40. A tank for storing fluids, comprising a vessel and a reinforcing frame extending over the sides of the vessel, the frame having a top and a base wherein the vessel is retained in the frame by removable keys that connect the top of the frame to the base. 